Project Summary Cardiovascular disease is responsible for more than 600,000 deaths each year in the US, and more than half of these are due to coronary heart disease (CHD). Myocardial perfusion imaging (MPI) is one of the most effective tools for assessing CHD, and according to the most recent estimate, this technique accounts for >50% of all nuclear medicine studies in adults, nearly 6 million scans in 2014. At present, most of these studies are carried out using 99mTc-MIBI and 99mTc-tetrofosmin, despite the significant limitations of SPECT (single photon emission computed tomography) for MPI including lower spatial resolution than PET (positron-emission tomography); the lack of routine attenuation corrections, which are of particular importance in an increasingly obese population; and the challenge of measuring myocardial blood flow (MBF), which is critical to accurately evaluating global ischemia and microvessel disease. This investigation, ?A Novel F-18 PET Myocardial Perfusion Radiopharmaceutical based on Rhodamine Dyes,? builds upon a currently funded project of the same title, 1 R01 HL108107-01, that concludes on 1/31/2017. As in the foundational R01, the primary objective of this project is to develop an 18F-labeled radiopharmaceutical for PET imaging of myocardial perfusion. The Specific Aims of the original project have been largely fulfilled; and thus, while our central hypothesis remains the same, i.e., that a PET myocardial perfusion imaging agent can be developed based on an 18F-labeled rhodamine dye, we have gathered sufficient preliminary results to initiate a first-in- human-study in the next project period. We have demonstrated that 18F-labeled rhodamine dyes accumulate impressively in the heart, which confirms their significant potential as PET MPI radiopharmaceuticals. The central hypothesis of this proposal is, therefore, unchanged: A PET radiopharmaceutical for the evaluation of myocardial perfusion can be developed based on an 18F-labeled rhodamine dye. We have tested and validated this basic premise in our laboratory and found that the 18F-labeled diethyleneglycol ester derivative of rhodamine 6G ([18 F]Rho6G) shows very high accumulation in the heart, minimal accumulation in the liver, and rapid blood clearance. While 18 F-Rho6G has shown great promise as an MPI agent, we do not yet know if it will perform optimally in humans. Thus, we will explore additional rhodamine-like compounds as potential PET radiotracers for MPI. Accordingly, the new Specific Aims will first build upon our findings with 18F- Rho6G by a) carrying out a first-in-human study with [18F]Rho6G; b) measuring the extraction fraction of 18F- Rho6G, a critical parameter for a clinically useful MPI radiopharmaceutical; and c) evaluating a number of novel rhodamine derivatives and also assessing alternatives cores in anticipation of the possible need for an alternative to rhodamine dyes for human use. Our successful accomplishment of these Specific Aims will lead to the development of a novel and effective PET radiopharmaceutical for MPI that will significantly improve clinical management of patients with CHD by providing an accurate measure of myocardial perfusion.